1. Field of the Invention
The present invention relates to a constant velocity joint.
2. Description of the Related Art
A constant velocity joint is known to have an outer joint member having a plurality of raceway grooves extending in an axial direction, and an inner joint member having a plurality of leg shafts inserted in the raceway grooves. Japanese Patent Application Publication No. 2012-197832 (JP 2012-197832 A) discloses a tripod shaft (leg shaft) in which a recess groove is formed between a torque transmission surface having a circular cross section and a seat protruding outward in a radial direction with respect to the torque transmission surface. The recess groove is a portion formed to prevent interference with an end portion of a shaft-like rolling element, which rolls on the torque transmission surface. The recess groove is recessed inward in the radial direction with respect to the torque transmission surface, and has a concave surface.
A base portion of the tripod shaft is a portion on which stress concentrates, and thus needs high strength. In the technique described in JP 2012-197832 A, however, if a curvature radius of the recess groove is decreased, the stress concentrates on a portion in which the recess groove is formed, reducing the strength of the base portion of the tripod shaft. In contrast, if the curvature radius of the recess groove is increased, a connection position between the recess groove and the torque transmission surface is positioned closer to a leading end side of the tripod shaft. In this case, the axial length of the torque transmission surface is reduced, and thus a contact area between the torque transmission surface and the shaft-like rolling element is reduced. This causes wear of the torque transmission surface and the shaft-like rolling element, possibly deteriorating torque transmission efficiency.